1. Field of the Invention
The present invention relates to well treating fluids such as completion and production stimulation fluids, and more particularly, to methods of controlling the rates of release of liquid chemical additives in well treating fluids.
2. Description of the Prior Art
Hydraulic cement slurries are commonly utilized in primary well cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, a cement slurry is pumped into the annular space between the walls of the well bore and the exterior surfaces of the pipe string disposed therein. The cement slurry is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
A variety of chemical additives are utilized in cement slurries used for carrying out primary cementing and remedial cementing operations in wells. Examples of such additives include cement slurry set accelerators, cement slurry set retarders, cement slurry fluid loss control additives, cement slurry dispersants and the like. While the chemical additives utilized in cement slurries function to produce desired results, problems are often encountered as a result of the chemical additives producing the results too quickly. For example, in cementing pipe strings in subterranean formations having low temperatures, the cement slurry often needs to be accelerated to reduce the time required for the cement slurry to set at the low temperatures. However, if the set of the cement slurry is accelerated too much, it can result in an insufficient time to pump the cement slurry into the subterranean location to be cemented. It is desirable in such applications to have a long cement slurry pump time, but once the cement slurry is placed, the time required for it to set should be short. While various methods have been developed and used heretofore for delaying the release of chemical additives used in well cement slurries of the types described above, there is a continuing need for improved methods which are reliable and easily accomplished.
A variety of other well treating fluids are utilized in the construction of wells as well as in the production and stimulation of hydrocarbons therefrom. The most commonly used such treating fluids are viscous liquids of various types. For example, viscous liquids are utilized as fracturing fluids which are pumped into producing formations at rates and pressures such that fractures are created and extended therein. Propping material such as sand is typically deposited in the fractures so that they are prevented from completely closing and provide flow passages through which hydrocarbons readily flow. Viscous fluids are utilized in a number of other completion and stimulation procedures performed in wells including forming gravel packs in well bores, fracture-acidizing producing formations and the like. In order to reduce the viscosities of the viscous liquids utilized in such procedures so that the liquids can be removed, delayed viscosity breaking chemical additives must be included in the viscous liquids.
Polymeric compositions are also utilized as well treating fluids. For example, polymeric compositions have heretofore been used to reduce or terminate lost drilling fluid circulation and the undesirable flow of water or gas into or from a subterranean zone penetrated by a well bore. Such compositions are introduced into the subterranean zone to be sealed and caused to polymerize and cross-link therein whereby a stable sealing gel which reduces or terminates the undesirable fluid flow into or from the zone is formed therein. The polymeric compositions must include polymerization initiators which are delayed whereby the polymeric compositions can be pumped into the zone to be sealed before polymerization takes place.
The above described chemical additives along with a variety of others are utilized in well treating fluids, the release of which must often be delayed or otherwise controlled in order to accomplish desired results. Thus, there are continuing needs for improved methods of controlling the rates of release of chemical additives in treating fluids introduced into wells.